The present invention relates to a heat development system. More specifically, the invention relates to a heat-developable photographic light-sensitive material which is excellent in storage stability (shelf life) with the passage of time and has a good antistatic faculty.
In a recent medical treatment field, from the view points of environmental preservation and space saving, the reduction of the amount of the treated waste liquids has been strongly desired. Therefore, the techniques in regard to heat- developable light-sensitive materials (photosensitive heat- developable photographic materials) for medical treatment diagnoses and photographic techniques capable of being efficiently exposed by a laserxe2x80xa2image setter or a laserxe2x80xa2imager and capable of forming clear black images having a high resolution and a high sharpness have been required. In these heat- developable light-sensitive materials, solution-type processing chemicals are not used and a heat-development system, which is simpler and does not spoil the environment, can be supplied to customers.
Heat-developable light-sensitive materials are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and Klosterboer, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d A, xe2x80x9cImaging Processes and Materialsxe2x80x9d Neblette, 8th edition, edited by Sturge, V. Walworth, and A. Shepp, Paragraph 9, page 279 (1989). Such a heat-developable light-sensitive material contains a reducible light-sensitive silver source (e.g., an organic silver salt), a photocatalyst (e.g., a silver halide) of a catalytically active amount, and a reducing agent of silver in the state of usually being dispersed in an organic binder matrix. The heat-developable light-sensitive material is stable at normal temperature but after exposure, the heat-developable light-sensitive material is heated at a high temperature (for example, at least 80xc2x0 C.), silver is formed through the oxidation- reduction reaction between the reducible silver source (functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by the catalytic reaction of an electrostatic latent image formed by the exposure. Silver formed by the reaction of the reducible silver salt in the exposure region provides a black image, which is in contrast with non-exposed regions to form an image.
On the other hand, the technique of a semiconductor laser, which has recently been rapidly progressing, has been applied to a heat-development image-forming apparatus of outputting diagnosis images for medical treatment and small- sizing the apparatus and quickness have been realized. However, with small-sizing of the apparatus, conveying route of heat- developable light-sensitive materials has been complicated. That is, because the heat-developable light-sensitive material is transferred by many rollers made of various materials, dusts attach thereto by static electricity formed at transferring to soil the image information, which increases the danger of causing a wrong diagnosis at present. Particularly, when the conveying speed at the conveying member before exposure is fast, dusts, etc., are more liable to be attached, whereby a correct image exposure is not carried out to give very serious problems.
For preventing the generation of static electricity, a high-molecular electrolyte and an ionic surface active agent has hitherto been used but because these compounds have a large hygroscopic property, there are problems that the humidity reliance of the antistatic effect becomes large and also the environmental temperature and the humidity reliance at exposure and heat development are deteriorated. Also, when a crystalline metal oxide is used for static prevention, there is a problem that the Dmin has hitherto been increased. Particularly, because in the case of a heat-developable light-sensitive material, a fixing treatment is not carried out after heat development, there is a problem that the extent of increasing the Dmin is large. Furthermore, different from ordinary photographic light-sensitive materials using silver halides, there is a problem of increasing the formation of fog in the product form.
In view of these problems in the techniques of prior art, an object of the invention is to provide a heat-developable light-sensitive material, which is excellent in shelf life with the passage of life and shows a good antistatic faculty in a heat development system of forming images using a heat- development image-forming apparatus having quickened conveying members. In particular, an object of the invention is to provide a heat-developable light-sensitive material, which gives less increase of the formation of fog even in the case of using after storing for a long period of time and gives less white spots of images owing to the excellent antistatic characteristics in the heat development system.
As a result of making various investigations for solving the above-described problems, the present inventors have found that the above-described objects can be attained by the following invention.
That is, the present invention is a heat development system of forming images by exposing and heat developing a sheet-form heat developable light-sensitive material comprising a support having on one surface thereof a binder, an organic silver salt, a reducing agent for silver ion, and light-sensitive silver halide grains by a heat development image-forming apparatus, wherein the conveying speed in the conveying member of conveying the heat developable light-sensitive material from the light-sensitive material-supplying member to an image exposure member in the heat development image-forming apparatus is 1 meter/minute to 5 meters/minute, the sum total content of the organic silver salt and the heat-developable light-sensitive silver halide in the light-sensitive material is 1 g/m2 to 2 g/m2 in terms of Ag, and the heat-developable light-sensitive material has at least one back layer in the opposite side to the surface having formed thereof a heat-developable light-sensitive layer containing the light-sensitive silver halide grains, has an electrically conductive layer having dispersed in a binder at least one kind of a crystalline metal oxide selected from ZnO, TiO2, SnO2, Al2O3, In2O3, SiO2, MgO, BaO, and MoO3 or a composite oxide of them, and the lateral resistance thereof under the environment of 25xc2x0 C. and a relative humidity of 10% is not larger than 1011xcexa9.
In the heat-developable light-sensitive material used for the heat development system of the invention, it is preferred that the electrically conductive layer is formed at least at the position between the heat-developable light-sensitive layer and the support and between the back layer and the support. Also, it is preferred that the lateral resistance thereof under the environment of 25xc2x0 C. and a relative humidity of 10% is not larger than 1010xcexa9. The heat-developable light-sensitive material is particularly useful for a medical treatment diagnosis.